The invention relates to a method for insulating coils provided in rotary electric machines.
The following methods of insulating coils in high-voltage rotary electric machines are known in the art:
(1) In a first method, insulating tape is wound on a coil having a hexagonal form. The formed coil is then put in an impregnating tank where it is impregnated with resin under vacuum.
(2) In the second method, preformed coils are inserted into the slots of the iron core in the rotary electric machine and the leads are connected. After being subjected to an insulating treatment, the iron core with the coils is put in an impregnating tank where the coils are impregnated with resin under vacuum. Then, the resin is solidified by heating, thus forming an insulating layer. The second method is the so-called "post impregnation method".
(3) In a third method, insulating tape containing much resin is wound on each coil. The coil thus treated is heated and pressurized to provide an insulated coil.
The coils manufactured by the above-described methods have substantial insulating properties. However, the first and second methods are disadvantageous in that it is necessary to use a vacuum impregnation device, and the third method suffers from a drawback in that it requires the heating and pressurizing devices.
The coils of a high voltage rotary machine are generally hexagonal. Accordingly, in any one of the first, second and third methods, the work of winding a coil end including a coil end part, coil end nose, wiring parts and phase rings must be manually carried out for the most part. Accordingly, a large number of intricate manufacturing steps are required. Furthermore, the work of winding insulating tape on the coil is time consuming. Thus, there has been a strong demand for the provision of a method in which the coil can be insulated without using tape.
In addition, in the above-described methods, the coil end cannot have a sufficiently high insulating property when hardened by heating, and almost all faults due to poor insulation occur at the coil end. It is considerably difficult to satisfactorily insulate the coil end.
For instance, in a conventional post impregnation type coil insulating method employed extensively for rotary electric machines, preformed coils are wrapped with insulating tape and are then inserted into slots cut in the iron core of the rotary electric machine. The leads of the coils thus treated are connected, and the connecting parts thereof are then wrapped with insulating tape. Thereafter, the coils thus laid around the iron core are set in the impregnating tank and impregnated with insulating varnish under vacuum. Then, the insulating varnish thus applied is hardened by heating in a drying oven, thus forming an insulating layer.
As shown in FIG. 1, each coil 5 comprises slot parts 1; coil end parts 2; nose parts 3; and lead parts 4. In the post impregnation coil insulating method, all of these parts 1, 2, 3 and 4 are wrapped with mica tape so that an insulating layer 6 is formed thereon. Thereafter, as shown in FIG. 2, the coil 5 is inserted into a slot in an iron core 7. The lead parts 4 are connected to phase rings 8 and the connecting parts thereof are wrapped with mica tape so that an insulating layer 6 is formed thereon. In order to support the coil end parts 2, a spacer 9 is inserted between the coil end parts 2, and a brace ring 10 is coupled to the outer end portions of the coil end parts 2. Thereafter, the assembly of the coils and the core is set in the impregnating tank. Under this condition, the coils are impregnated with insulating varnish under vacuum, and the insulating varnish thus applied is hardened by heating in the drying oven, thus forming an insulating layer 6.
In the above-described conventional method, before the coil is combined with the iron core, the slot parts 1 and parts of the coil end parts 2 can be wrapped with mica tape by using a machine such as a taping machine. However, winding the mica tape on the nose parts 3 and the lead parts 4 and on the connecting parts of the lead parts 4 and the phase rings 8 after the coils 5 have been inserted into the core 7 must be carried out manually. Thus, the work of winding the mica tape on these parts is low in efficiency, and time consuming. Moreover, the formed insulating layer 6 does not always have a sufficient insulating property even after the impregnated insulating varnish has been hardened by heating. Again, almost all faults due to poor insulation occur at the coil end.